Process for making felt-like products



v- 1956 H. A. sEcRIsT 2,774,126

PROCESS FOR MAKING FELT-LIKE PRODUCTS Original Filed Nov. 4. 1950 INVENTOR. HOP/46E H SEC/ewe:

United States PRocEss FoR MAKING FELT-LIKE rnonucrs Horace A. Secrist, Dedham, Mass, assignor to The Kendall (Jompany, Boston, Mass, a corporation of Massachusetts Original application November 4, 1%50, Serial No. 194,195. Divided and this applicationMarch 5, 1956, Serial No. 569,349

2 Claims. (Cl. 28- 723) Many attempts have been made to manufacture nonwoven fabrics by mixing cotton fibers andfusible fibers by some suitable means and thereafter activating the fusible fibers. Among the successful materials made in this manner is the fabric disclosed by Reed in U. S. Patent 2,277,049. According to the preferred process of Reed, carded webs of intermingled cotton fibers and plasticized cellulose acetate fibers are unified by heat and pressure to form a fabric. Although this material and structures similar to it have enjoyed a wide variety of commercial uses, they still suffer from certain undesirable characteristics. The heat and pressure usually required to produce a strongly unified sheet material have caused the mixed fiber products of the prior art to lose thick ness and have a somewhat harsh and papery feel. The primarily lengthwise alignment of fibers obtained by the carding or garnetting process persists through to the finished product resulting in a highly directional fabric with a high ratio of lengthwise to widthwise strength, often of the order of 9 or 10 to 1. The extensibility is of the same order of magnitude as that of an untreated web or bat, namely or less. 7

It is the primary object of this invention to provide a novel soft, porous, extensible felt-like sheetmaterial having various advantages over the product just described and it is a special object of this invention to'produce a reinforced cotton feltof high tensile strength in both the Wet and dry states.

I accomplish these objects and others by supplying a sheet material comprising a network of intermingled cot ton fibers and fibers having latent coalescent properties, the cotton fibers being frictionally entangled and interlocked with each other and with the fusible fibers in situ by artificially induced kinks, bends, twists and curls, and the fusible fibers'being bonded to one another and/ or the cotton fibers by coalescence. Depending upon the conditions of caustic treatment, the percentage of fusible atent 'ice 2 of said cotton fibers, and coalescent fibers 12 which are commingled with the aforementioned cotton fibers, and which are adhesively bonded to some, at least, of the points of intersection of said coalescible fibers with each other and with the said cotton fibers.

The source of the integrity and coherence of my sheet materials is the frictional interlocking provided by the network of the curled and kinked cotton fibers, and the positive adhesive fiber-to-fiber bonding supplied by the fusible fibers which co-operate to give my products a combination of conformability, extensibility and strength.

The adhesive bonds act as a framework permeating the structure, impeding and damping the inter-fiber adjustments which take place as my sheet materials are stressed. As the curled and kinked cotton fibers straighten, extend,

and slip past one another, they assume in many cases new positions of entanglement with each other and with the fusible fibers, thus stabilizing the fabric and providing capacity for further extension before break.

Even though my finished fabrics are usually prepared from highly oriented carded webs, they are usually sub stantially more balanced than the fused fiber webs of the prior art because the three-dimensional frictional interlocking and entanglement of the cotton fibers in situ tends to randomize the orientation of the fibers. Individual fibers are less likely to be displaced or removed from the structure by abrasive forces, and in a direction normal to the plane of the sheet material the entanglement of the fibers greatly enhances the resistance to delamination of my products, particularly in those instances in which they have been prepared from a plurality of carded webs.

Because of their substantial tensile strength and other characteristics, my products are useful inthe medical and surgical field as sponges, dressing pads, bandages and the like. No separate fusing treatment may be required because the activation of some fusible fibers may be effected by standard heat sterilization procedures employed in the preparation of bandages andthe like in hospitals. Many of the sheetmaterials of this invention, prior to substantial activation of the fusible fibers, have distinct products of my invention may vary from soft, fiuify, absorbent, highly extensible materials to structures of limited extensibility and/or increased stiffness.

These and other characteristics of my invention will be more readily appreciated from the following description of an embodiment thereof selected for the purposes of illustration, and shown in the accompanying drawings in which:

Figure l is a plan view of a section of a fabric of my invention, and

Figure 2 is a cross section along line 22 of Figure 1. As shown in these drawings, the fabric is made of a three-dimensional network consisting essentially of cotton fibers 10' which are frictionally interlocked and entangled with themselves and each other as a result of chemically induced random kinks, twists, bends and curls advantages in the manufacture of shaped liner or covering materials, stifi'eners, and stiifened shaped articles.

Their conformability, and extensibility enable them to be marginal tear resistance and interior softness and absorbency are required, as, for example, sanitary napkins and diapers. In making such products, the sheet material may be cut to the desired'shape and heat pressed at its edges only, thereby activating the fusible fibers in these areas While leaving a soft, fiuify absorbent interior region.

The fusible fibers contained in my structures may be selected from a very wide variety ofmaterials. For'example, various fibers comprising esters and others of cellulose are suitable, such as those made of cellulose acerate, cellulose propionate, cellulose butyrate, ethylcellulose and benzyl cellulose. Fibers made of mixed esters, such as cellulose acetate-propionate, also are very useful. Others of an'entirely different chemical nature, however, may be employed, such as those made of vinyl polymers, for example, polyvinyl chloride, polyvinyl acetate, polyvinylidene. chloride, or vinyl copolymers, and those'of the polyamide type, an important example of which is that commercially known as nylon. The above mentioned fusible fibers may be classified as thermosensitive;

to treatment with alkaline liquids-having a substantial swelling action on cellulose in such a manner as to per:

mit'shrinkage of the structure, these steps of the 'process and an apparatus useful incarrying these out berng more fully disclosed in my copending application, Serial No. 643,799, filed January 26, 1946, now U. S. 2, 528 793, issued November 7, 1950,- of which this 'applicatron is a continuation-in-part. The assembly is then washed to remove the swelling agent and dried. 'Depending on their nature the fusible fibers may be activated by the alkaline treatment, by the heat employed in the drying process, by subsequent heat treatment or by the' action ofappropriate solvents or by suitable combinat1ons thereof. Pressure may be used to increase the bonding by the activated fibers. The preferred treating chem cal for the cotton fibers is an aqueous solution of caustic alkali such as sodium, potassium or lithium hydroxide, but other basic cellulose swelling agents may be 'employed,'such as solutions of sodium zincate, quaternary ammonium bases such as benzyl trimethyl ammonium hydroxide and the like.

'Usmg aqueous sodium hydroxide solutions satisfactory results have been obtained with solution concentrations of at least 8% and less than 30% NaOH at ternperatures from'iust above the freezing point of the solution to l-25 C. It should be understood that temperature and concentration are mutually dependent varimay fix the operating range of the other. Preferably and for best results such solutions are used in concentration minutes and the fiber sheet is then removed from the vat.

In my preferred material the fusible fibers are thermoplastic in character and substantially inert to my alkaline treating agent under the temperature, concentration, and time duration condition of my process. The duration of contact of the fusible fibers with the treating solution is particularly important in the case of thermoplastic fibersof a cellulosic nature such as cellulose acetate where prolonged contact might radically change the characteristics of the fibers, reducing or destroying their thermoplastic properties. Also, fibers of this type may in some instances be rendered coalescent in the caustic solution, depending on the particular fiber and conditions of treatment, causingbonding of the fibers Yprior to heat or solvent activation. Usually, however, the bonding supplied by the fusible fibers as a result 1 of the caustic-treating stage of my process is only inci-' dental, and the fusible fibers retain their latent coalescent properties-to a substantial extent;

The particular type of thermoplastic fiber "chosen depends primarily on the character of the 'productdesired. In order to produce a flutfy, highly extensiblestructure' the fusible fibers of which are to beactivated at some point in the end use of thematerial, I select a fusible fiber which becomes tacky and coalescent at a relatively high temperature so as to minimize the. activation of the fusible fibers in the drying of the sheet material following caustic treatment. It is possible, of course, to achieve these same results with fibers which become tacky at 'ables and that the selection of a particular value forone and treated to remove the chemical; preferably promptly 'as overlongexposure to the chemical may. produce uridesirable gelatinization of the fibers.

The extent of fiber curling, kinking, and entanglement 'in situ, after the mixing and sheeting of the two classes of thefibers, and upon which the unique features of this 7 invention are dependent, is indicated roughly bylthe'permanent area contraction of my sheet materials during though products whose area shrinkages arevless may possess someor many of the features of this invention.

The amount of shrinkage obtained depends on a num-,

ber'of. factors, the most important of which' are the weight perunit area of the fibrous assembly to be treated,

shrinkages'decrease if either the weight of the assembly. or the relative proportion of fusible fibers tocotton fibers is increased. For mostproducts of this invention, the cotton fibers should be in' major proportion in order to i have, the greatest flexibility of operating conditions, al-

though satisfactory shrinkageshave' been observed with cotton fiber concentrations somewhat lower than percent in conjunction with optimum values of the other.

factors influencing area contraction of the assembly.

lower temperatures by reducing the drying temperature, but this is inefficient from an operating viewpoint. Conversely, if a product is desired in which thefusible fibers are partially or completelyactivated, the drying temperature may be increased, or a fusible fiber may be selected which becomes tacky and coalescent at a relatively low temperature. j

'The operation of activating the fusible'fibers should be controlled in accordance with the nature of the binder fibers used, the proportion of suchfibers, and the characteristics of the final product desired. During themixing step these fibers can beina dry free condition; suitable for dry assembly, picking, carding or like processes. Conproduce good softening action. 'Those found most prac 'tical consist of'heat, solvents orf those substances such as'plasticizers which exert a softening action, or some combination of the foregoing; Where the binder fibers are thermosensitive, having the property of being softened 'by heat and hardening upon cooling again, these changes in the physical condition ordinarily take place without the first stage of my process; I have found that the most". 7

satisfactory results have been obtained when'this con traction is of the order of 30 percent or greater, al-

any material chemical deterioration, Accordingly,- a convenient; method of eifecting activation is to pas's the f sheet material through a heating ohamber, 'between heated plates or heated rolls, or through fany other. suitable ap-' paratuspsuch as a dielectric-heating unit, capable of raising the temperature of the fibers to the desired degree. 'Where the binder'fibersused are soluble in "onmay be softened by-Organic solvents which do'not'aifect the ,cotton fibers'to any substantial degree, another method of producing the desired union'fof the fibers consists in' subjecting the material after caustic treatment t'othe action 'of such a solvent, or "to a solvent vapor pr 'gas, which wilLdevelop in situthe adhesive or bonding rop- 'erties of the fusible fibers;- 'For instance, if the sheet m'a t erial consists of a mixture of cottonand cellulose acetate fibers it may be treated With a mixture of acetorie "and, V V fmethanol to superficially dissolveor soften the fusible fibers Theweb may then be passed between pressure ,7 rolls. The nature of the solvents employed necessarily will be determined by the character of the binder fibers and other practical considerations. fsolven'ts for the various fibers abovementioned are known, including acetone, methyl alcohoL Yrnonornethyl ether of ethylene glycohpr opylene:oxide,.'inethyl acetate,

A wide variety "of acetic acid, diacetone, chlorobenzene, dimethyl formamide, chloroform, toluene, and diethyl ether, the particular solvent chosen depending on the chemical composition of the binder fiber employed. 7

Whether or not pressure be used in the activation process will depend chiefly upon the nature of the fusible fibers used and of the character of the final product desired. Pressing necessarily results in bringing a single fusible fiber in contact with a greater number of contiguous fibers of both kinds than otherwise would be the case and thus to increase the number of individual bonds with accompanying increase in strength. It tends to reduce the softness, flexibility and draping qualities of the product and to give it greater firmness and rigidity. Whether to use pressure and the degree of pressure to be employed, if it is used, therefore will depend upon results desired, the nature of the fusible fiber andsoftening agent used and other practical considerations.

That the nature of the bonding, coalescence or. association of the fibers with each other produced by the activation process may take several forms will be evident from the character of the activation processes herein described. For example, in subjecting the sheet material to a suitable temperature the thermoplastic fibers will attain a softening stage which is sufiicient to develop the coalescent properties. Or with some types of binder fibers, the heating step may be carried further until the surfaces of the fiber become sticky, so that when the web is pressed the binder fibers will adhere or weld firmly to other binder fibers, and they likewise adhere to the nonbinder fibers with which they are in contact. Or with some kinds of fusible fibers the heating step may be continued still further until the form of the binder is further broken down and the fibers are converted into almost a liquid state, in which case, they will wet intersecting non-binder fibers and will unite them upon sub sequent cooling. In any of these extremely soft conditions more or less spreading the binder constituent may be effected, if desired, and even to such a point as to convert some or almost all of the fusible fibers into discreet particles or a discontinuous or continuous nonfibrous film.

In those instances where heat is employed as an activating agent for'the fusible fibers, it is possible to obtain more uniform bonding action throughout the sheet material by matching the thermo-softening point of the fusible fibers to the temperature gradient throughout the thickness of the web. This matching may be accomplished by incorporating different amounts of plasticizer into fusible fibers in the various strata of the sheet material, or by selecting chemically different fusible fibers with varying softening temperatures.

When my products are prepared with a relatively high proportion of thermoplastic fibers at, at least, one surface of the material, they are useful for purposes to which heat scalability is desired, as for example, in porous or permeable containers. Sheet materials which exhibit difierent surface characteristics because the fusible fibers occur in predetermined difierent proportions on opposite surfaces are particularly useful as adhesive tape backings because good interface adhesion and resistance to picking on unrolling are secured.

By incorporating yarns or woven fabrics into my structures prior to caustic treatment, it is possible to manufacture products similar to those described in my copending application 8/ N 191,933, filed October 24, 1950. In these products the positive adhesive bonding supplied by the fusible fibers considerably strengthens the frictional entanglement of the spur; and unspun fibers A class of fusible fibers may be used which are not thermosensitive, but'which swell and become gelatinous and tacky in the presence of the alkaline treating agents 7 of my process. Examples of this class are fibers of regenerated cellulose manufactured according to the vis cose or cuprammonium processes. One advantage inherent in the use of this class of fibers is that no aftertreatment of :the'material is required. The cotton fibers are curled and kinked and the fusible fibers activated by the same treating solution. The extent of activation of this type of fusible fiber may be controlled by varying the temperature and concentration of the caustic, or by adding varying amounts of sodium chloride to the wash water, or to the caustic. Products of this type have a high degree of stability, because the adhesive bonding provided by the regenerated cellulose fibers is substantially unaffected by heat or the action of a wide Variety of organic solvents.

The following examples'are given as illustrative of the products of my invention:

Example 1 Nineteen parts by weight of bleached cotton fibers were mixed in a picker lapper with one part Vinyon fibers VYI-IH-Z (a co-polymer of vinyl acetate and vinyl chloride distributed by The American Viscose Company). The lap was fed to a card which carded the fiber mixture and worked it into the form of a web. Several such webs were superposed to form a fibrous sheet weighing approximately 70 grams per square yard. The fibrous sheet was cold-pressed by passing it between calender rolls at a pressure of about 1000 pounds per inch of roller width and then treated in a bath of 14% NaOH at a temperature of '4 C. for a period of about 35 seconds. The material was removed from the bath, rinsed with water, neutralized with dilute acetic acid, again washed, and dried in air. An area shrink of 77% was noted. Half'of each sample was fused between layers of cheese cloth at 300 F., for five minutes without pressure and the following physical properties determined.

Q ORRECIED STRENGTH 1 Unfused Fused Dry Wet Dry Wet Lengthwlse (machine direction) 7.10 2.36 7 02 3.38 Wldthwise 27 45 944 2 36 1 27 Ratio (Lengthwise to Widthwise)- 2. 2. 51 2 97 2. 66

ELONGAIION, PERCENT Lengthwisc 89 as 93 Widthwise 112 94 110 1 Corrected strength: In making comparisons between felts of difierent thicknesses and densities I make use of what I term corrected strength, which is the actual load at break (in pounds per inch of width of the sample tested) divided by the weight in pounds of one square yard of the felt. This corrected load takes into account difierences in weight 0! the compared felts, in effect, giving the approximate strength of a unit quantity or weight of fibers on different felts.

Example 2 I A fibrous sheet material containing 10% by weight Vinyon fibers and 90% cotton fibers was prepared, treated and tested as'in Example 1. The area contraction was 7 Example 3 A fibrous sheet material containing 2 by weight Vinyonfibers and 80% cotton fibers was prepared, treated and tested as in' Example 1. The area contraction was CORRECTED STRENGTH Uniused Fused Dry I Wet Dry Wet Lengthwise 7.02 3.24. 17.8 "1012' widthwisann; 1.31 .666 4.53 2.70 Ratio (Lengthwl o 0 Widthwise 3. 93 4.97 15.94. 3.73

ELONGATION, PERCENT r'en tnwise.;-;;-.-.; "'53 4s 37 4a 1 Widthwise 100 114 :77 44 Example?! fibrous sheet material containing 40%" by weight Vinyon fibers and 60% cotton fibers was prepared, treated containing 10% by weight Vinyon fibers and 90% cott bs awa Pr d and te s n E a le! except that nip rolls at a pressure of about ten pounds per inch of roller width were substituted for the heavy. calender rolls. The area contraction of the air-dried material was 72.6%. The following physical properties were determined: i

. 1 V Corrected strength 'Lengthwise 8.48 Widthwise 2.36 Ratio 3.59

5 V Elongation, percent Lengthwise f l 55.7 .Widthwise 1 ,70.4

l V 7 Examplej6 V A 10% Vinyon 90% cotton fibrous sheet weighing 30 grams per square yard. wasprepared according'to .the .method of Examplel and given a light pressby passing .it. through nip rolls. at .a; pressure of about ten pounds ,per. inch of roller width. The sheet was then treated in ,a bath of. 18.4%..Na0H at 10..C. washedwithwater, neutralized with dilute acetic acid, and againwashed with jwater. area contraction of about 38%,was observed. iAportion'of thematerialwas air-dried and the remainder dried on'asteamfcan maintained vat about'225" F; Part p e aned' o ,w. u i d o Per nne .rninute to a pressure of 386 pounds ,per square inch between metal plates heated to' 2.95 fjThejfollowing 5. physical properties of each .materialwere determined: V

CORRECTED STRENGTH Air 'Can 5 'Hot Dried lDried, Pressed Lengthwise 11.6 10.8 41.2

YELONGATION, PERCENT Lengthwisc 20.9 2 0.9 13.9 Widthwise 44.1 72.4, 0. 2

'Example7 V A 40% Vinyon, cotton fibrous sheet weighing 108 7 grams per square yard was prepared according'to the method of Example 1' and given a lightpressby passing it through nip rolls at a pressure of about ten pounds per inch of roller width. The sheet was then treated; in a bath of 13.8% NaOH'at 4 C., washed with water, neutralized with'dilute 'acetic acid, and again washed'with water. An area'shrink of 62.5% was noted; A portionfi of the material was air-dried and the remainder dried on a steam can at a temperature of about 225 F. Part of the can-dried portion was subjected for a period of'one minute to a pressure of 22.1 pounds per square inch between metal plates heated to 290 F. The following physical properties of each material were determined:

CORRECTED STRENGTH.

Hot 7 Pressed Air 7 Dried Can Dried Lengthwise Widthwise ELONGATION; PERCENT LengthwiseiuL i 10. 62.

Widthwise 1 Example 8 V ;A fibrous sheet weighing44 grams I per 1 square yard I 7 consisting of bleached cotton fibers and 20 percent]:

fusible fibers composed-of two parts cellulose acetat and one part paratoluene ethyl sulfonamide was prepared according to the method of Example 1 and given a light press by passing it through nip .rolls at a pressure of about" ten'pounds per'inch of roller width. The sheet was then treatedin a bath of 11.7% NaOH' at +2 C.,' washed with water, neutralized with dilute acetic acid, and again washed with water. An area shrink of 62.3%v was ob-. served. A portion of thematerial was air-dried and the remainder dried on a'steam can maintained at about 225 'F. Part of the can-'dried'portion was sprayed with acetone, pressed with a'cardboard roller under. hand pres sure and dried on the steam can. 7

. noticeably stiffer and stronger than either of the other The product was samples. The followingphysical properties of each 'material'were determined: V p 5 CORRECT D sTR'ENCTHf .Air' fcan? Solvcnt- Dried 7 'Dricd. 'Fused' Lngtn ise 5 11.0 '8.7 19.3 Widthwise... 2.12 3.48 0.25 Ratio 5.2 2.50 2 09 E ONGATION, PERCENT Lengthwise"; f 17. 4 1:18.11 11.4 w aniwise 29.1 :10.1 ,1 1.e

Example 9 A fibrous sheet weighing 94.5 grams per square yard consisting of 60% cotton fibers and 40% viscose rayon fibers was prepared according to the method of Example 1 and given a light press by passing it through nip rolls at a pressure of about ten pounds per inch of roller width. The sheet was then treated in a bath of 20% NaOH at 21 C., washed with water containing 10% sodium chloride, neutralized with dilute acetic acid, again washed with water and dried on a steam can. An area contraction of approximately 30% was observed. The following physical properties were determined:

Example 10 A fibrous sheet weighing approximately 91 grams per square yard consisting of 60% cotton fibers and 40% viscose rayon fibers was prepared according to the method of Example 1, and given a light press by passing it through nip rolls at a pressure of about ten pounds per inch of roller width. The sheet was then treated in a bath of 20% NaOH at 21 C., washed with water, neutralized with dilute acetic acid, again washed with water and dried on a steam can. An area contraction of 56% was noted. The following physical properties of the material were observed.

Corrected strength Leng-thwise 14.0 Widthwise 4.76 Ratio 2.94

Elongation, percent Lengthwise 14.5 Widthwise 6.95

Present application is a division of my application S. N. 194,195, filed November 4, 1950, which is copending.

I claim:

1. The method of making an extensible, conformable, felt-like sheet material which comprises subjecting a body of cotton fibers intermingled with fibers having latent coalescent properties to the action of a liquid causticizing agent for cellulose at low temperature while supporting said body by means of said liquid agent substantially Without tensional stress and surface frictional restraint, thereby causing said cotton fibers to kink, bend, twist and intercurl; and contract said body in area, and removing said causticizing agent from the fibers without substantially stretching said body, and thereafter activating the fibers having latent coalescent properties so as to bond the two types of fibers at some, at least, of their points of contact.

2. The method of making an extensible conformable felt-like sheet material which comprises subjecting a body consisting essentially of cotton fibers intermingled with fibers of regenerated cellulose to the action of a liquid causticizing agent for cellulose at low temperature while supporting said body by means of said liquid agent substantially without tensional stress and surface frictional restraint, whereby the fibers are frictionally interlocked and entangled =by artificially induced kinks, bends, twists and curls in the cotton fibers and adhesively bonded at some, at least, of their points of contact by the coalesence of the fibers of regenerated cellulose.

No references cited. 

1. THE METHOD OF MAKING AN EXTENSIBLE, COMFORMABLE, FELT-LIKE SHEET MATERIAL WHICH COMPRISES SUBJECTING A BODY 